Rapid and wireless screening and health monitoring of materials and structures

ABSTRACT

Systems for screening and health monitoring of materials are provided. The system can include a material embedded with magneto-electric nanoparticles (MENs), a laser configured to direct incident laser light waves at a target area of the material, an optical filter disposed between the laser and the material, and an analyzer configured to detect the laser light reflected from the material.

STATEMENT OF GOVERNMENT SUPPORT

This invention was made with government support under Grant No.ECCS-093951 awarded by National Science Foundation. The government hascertain rights in the invention.

BACKGROUND

Materials play a key role in many modern application areas andindustries including electronics and magnetic information processing,civil engineering, medicine, and many others. In each of theseapplication areas, the notion of quality is largely defined by thequality of the materials used. It is not surprising that any technologyto rapidly screen and/or continuously monitor key materialcharacteristics, whether it is structural defects, quality of adhesivebonds, or purity of thin films and nano-structural compositions, wouldbe of great importance to any of the above industries.

BRIEF SUMMARY

Embodiments of the subject invention offer devices, systems, and methodscapable of wirelessly monitoring fundamental properties of materials anddevices at the nanoscale. Immediate and/or future applications includematerials health monitoring devices in electronics and magneticinformation processing such as the emerging field of spintronics, civilengineering, or medicine.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an illustration of a B-H loop scanning coil positioned todetect a signal from an integrated magneto-electric nanoparticle (MEN)structure.

FIG. 2 shows an illustration of a magneto-optical Kerr effect (MOKE)device positioned to detect a signal from an integrated magneto-electricnanoparticle (MEN) structure.

FIG. 3 shows an illustration of an alternating gradient magnetometerpositioned to detect a signal from an integrated magneto-electricnanoparticle (MEN) structure.

FIG. 4 shows a transmission electron microscopy (TEM) image of astructure containing magneto-electric nanoparticles.

FIG. 5 shows a plot of comparative magnetic hysteresis (M-H) curves inan in-plane orientation.

FIG. 6 shows a diagram of a magneto-optical Kerr effect (MOKE) deviceand a B-H loop scanning coil positioned to detect a signal from anintegrated magneto-electric nanoparticle (MEN) structure.

DETAILED DESCRIPTION

Embodiments of the subject invention provide systems, devices, andmethods for rapid wireless screening and health monitoring of nanoscalematerials and nanostructures. Magneto-electric nanoparticles (MENs) canbe integrated into materials or structures at a macro-, micro-, ornano-scale level to enable wireless monitoring of the health of thematerials or structures. As a result of a non-zero magnetoelectric (ME)effect, external magnetic fields can be applied to an existing materialor structure to induce a response from the MENs. This signal responsecan be used to monitor intrinsic electric fields, which underliemolecular bonds, stress effects in nanocomposites, structural defects,and other important properties. A change of an intrinsic electric fieldin the vicinity of MENs induces a change of the MENs' magnetization,according to the ME effect. The change in the MENs magnetization can beremotely (wirelessly) detected via traditional magnetometry approaches.Unlike other nanoparticles, MENs have both magnetic and electric dipolemoments, which are coupled together due to a relatively strongquantum-mechanical interaction. As a result, the electric dipole momentof the nanoparticle, p, is proportional to an external magnetic field,H. This can be based on the following isotropic relationship:p=αH,  (1)where α is the ME coefficient. In general, the ME coefficient is definedby an anisotropic tensor, α_(ij). However, the above simplifiedexpression is more than adequate for description provided herein.

Although electric fields underlie the most fundamental chemical bonds inmaterials, in general it is not possible to use electric fields towirelessly monitor the quality of the bonds. The externally generatedfields would interfere with the complex electric field background in theentire material and therefore, it would be difficult to separate theinformation carried by the electric fields due individual bonds from theinformation carried by the rest of the global electric field system. Onthe contrary, MENs embedded into the material, magnetic external fields,instead of electric fields, can be used effectively detect a signalresponse. The magnetic fields surrounding the MENs are not substantiallyaffected by an electric-field background. As a result, only theelectric-field-driven bonds close to the embedded MENs will contributeto the detected magnetic signal. Due to the non-zero ME effect, a changein the electric field profile results in a detectable change of theMENs' magnetization. Embodiments of the subject invention can detect amagnetic signal emanating from the local sites in the vicinity of MENsusing a number of existing magnetometry approaches, e.g., BH-looper,vibrating sample magnetometry (VSM), alternating gradient magnetometry(AGM), or magneto-optical Kerr effect (MOKE) magnetometry.

Embodiments of the subject invention can be used to measure mechanicalstress in thin film devices. At a fundamental physical level, the stresslocation and/or any resulting defect would induce a local electric fieldprofile change. In practice, such a local change is difficult to detectwithout attaching direct electrical contacts to the location of thedefect, which would make such a device impractical. On the other hand,magnetic fields can non-destructively propagate through both conductingand insulating materials as long as these materials are non-magnetic.Therefore, MENs can be embedded locally into a material used to convertlocal electric field changes resulting from a stress or a crack into amagnetic field which can be wirelessly detected. Consequently, MENs canbe used for monitoring the material's health at the nanoscale level towarn of an excessive stress or a potential crack at its very early stageof development.

Embodiments of the subject invention can use a local or globalmagnetometer (depending on a specific application) to propagateelectromagnetic waves towards a MENs integrated material and scan thesurface or the volume of the material to detect anomalous magneticsignature profiles characteristic of a mechanical stress or defect.Embodiments of the subject invention can use BH-loop measurements or thefocused magneto-optical Kerr effect (MOKE) to scan MENs integratedstructures, as illustrated in FIGS. 1 and 2, respectively.

For the BH-loop device, as seen in FIG. 1, a signal response can be dueto the change of the magnetic induction of a system of coils 110 in thepresence of MENs embedded in a sample 100 within a region around thecoil and the region being defined by the smaller radius of the coil. Inthis case, an AC signal in the range of from 100 Hz to over 1 GHz,depending on an application requirement, can be driven through theinternal single- or multi-turn coil 110. The number of turns can dependupon the required localization region of each scan point. An inducedelectromotive force (EMF) signal propagated through the external singleor multi-turn coil can detected at the same frequency. For manyapplications requiring low-frequency measurements, for example between 0and 1 kHz, a relatively large number of turns in both coils can be usedto increase the measurement signal-to-noise ratio (SNR). For a highfrequency application, the number of turns can be decreased, for exampleto below 100, thereby increasing the current, for example to above 10 A.The diameter of the inner circle can vary from a sub-mm to over a cm,depending on the required detection depth. In other words, the diametercan scale with the thickness of the scanned device. The diameter of theouter circle can be scaled comparably to the inner circle.

As seen in FIG. 2, a system can alternatively detect a Faraday rotationof the electromagnetic wave. A monochromatic laser source 210 directinga laser beam 220 towards the magnetic component of the MENs in thetarget material 200; the signal can be measured in the reflection ortransmission mode by an analyzer. Both sources can be used for rapidscreening through scanning the surface of a material under study. Again,many other embodiments are possible, including other magnetometryapproaches depending on the particular application.

Another embodiment including an alternating gradient magnetometer can beseen in FIG. 3. In this case, a scanner can include a nano-, micro-, ormm-size probe made from a non-magnetic solid material 320, such asquartz and the tip of the probe 320 can be made from a magneticmaterial. The probe attached to a piezoelement 310 is induced tooscillate at its resonant frequency by applying an AC voltage to thepiezoelement. The probe 320 can scan a sample surface 300 at a constantdistance, d, from the sample; the resonant frequency of the probe 320 isaltered by the interaction between the magnetic probe tip and themagnetic properties of the surface 300 in closest proximity to the tip,as illustrated in FIG. 3. The magnetic field generated by the MENs isaltered in regions containing a defect or a crack. As the magnetic tipof the probe 320 detects an altered magnetic field, the mechanicalresonant frequency of the probe 320 will change due to interaction withthe altered magnetic field. The nanoscale dimensions of the MENs canallow the device to detect the minute changes in the bond quality. Aresonant frequency of the probe 320 can be measured through theimpedance of a capacitive or inductive circuit supplying the AC voltageto the piezoelement 310 or using the reflection of an externalelectromagnetic source, such as a laser or a light emitting diode (LED),shining to a region on the probe 320 or the piezoelement 310.

FIG. 4 shows a transmission electron microscopy (TEM) image of MENsillustrating their structure. The MENs can be made of a ferromagneticcore of cobalt ferrite (CoFe₂O₄) with a piezoelectric shell made ofbarium titanate (BaTiO₃). The average size of the MENs in FIG. 4 isapproximately 30 nm. In some embodiments of the subject invention, theMENs can range in size from below 10 nm to over 100 nm. It should beappreciated by one of ordinary skill in the art that the MENs can bemade from any other composition with a non-zero ME effect andcompatibility with other materials. In preferred embodiments thenanoparticle crystal structure matches the crystallinity of the targetmaterials being monitored.

In order to fabricate the material embedded with MENs, a quantity ofMENs can be mixed with source material necessary to fabricate a targetmaterial. For example MENs can be integrated with an adhesive or abonding agent prior to hardening. The source material can then beprocessed to form the target material and deployed for a specificapplication.

A system for wireless screening and health monitoring can be seen in atleast FIG. 6. A laser producing device 410 can direct a light wavestowards a sample surface 400. The laser can be a diode laser having awavelength of 408 nm, 532 nm, and 650 nm. An optical filter or polarizer420 can be placed between the laser 410 and sample surface 400 to managethe specific polarization of light waves that are permitted to passthrough to the sample surface. An analyzer, for example a Kerrmicroscope or a MOKE detection system 430, can receive light wavesreflected of the surface of the sample. A change of the phase of thereflected light waves from the incident light waves is proportional tothe magnetization of the locally exposed region of the sample. Thesecond polarizer (not shown) can be positioned between the surface ofthe sample and the analyzer 430. In certain embodiments a single opticalfilter or polarizer can be utilized to filer incident light waves fromthe laser source to the material surface and reflected light waves fromthe surface material to the analyzer. The analyzer can detect adifference in the light polarization and intensity of the incident lightwaves and the reflected light waves.

Additionally, a power source, including a waveform generator, 440 can beelectrically connected to a single- or multi-turn conductive coil. Thewaveform generator can drive an AC signal through the coil therebyinducing a magnetic field. A magnetic field sweep or frequency sweep canbe conducted and the detected signal response can be used in order tocreate a localized M-H hysteresis loop. The M-H hysteresis loops can becompared to previously detected control loops to determine the health ofthe material at a target position. For example, MENs can saturate at arelatively small magnetic field on the order of 100 Oersteds (Oe), anelectric current on the order of a an Ampere (A) through a coil withapproximately 1000 turns and a diameter of 1 mm can generate a field onthe order of 1,000 Oe in the localized region of the sample material.

Embodiments of the subject invention can monitor a sample surface inpolar, longitudinal, transverse, and quadratic MOKE geometries. Forpolar MOKE detection the magnetic field of orientation is parallel tothe plane of incidence and normal to the sample surface. Forlongitudinal MOKE detection the magnetic field of orientation isparallel to the plane of incidence and the ample surface. For transverseMOKE detection, the magnetic field of orientation is normal to the planeof incidence and parallel to the sample surface.

The methods and processes described herein can be embodied as codeand/or data. The software code and data described herein can be storedon one or more machine-readable media (e.g., computer-readable media),which may include any device or medium that can store code and/or datafor use by a computer system. When a computer system and/or processorreads and executes the code and/or data stored on a computer-readablemedium, the computer system and/or processor performs the methods andprocesses embodied as data structures and code stored within thecomputer-readable storage medium.

It should be appreciated by those skilled in the art thatcomputer-readable media include removable and non-removablestructures/devices that can be used for storage of information, such ascomputer-readable instructions, data structures, program modules, andother data used by a computing system/environment. A computer-readablemedium includes, but is not limited to, volatile memory such as randomaccess memories (RAM, DRAM, SRAM); and non-volatile memory such as flashmemory, various read-only-memories (ROM, PROM, EPROM, EEPROM), magneticand ferromagnetic/ferroelectric memories (MRAM, FeRAM), and magnetic andoptical storage devices (hard drives, magnetic tape, CDs, DVDs); networkdevices; or other media now known or later developed that is capable ofstoring computer-readable information/data. Computer-readable mediashould not be construed or interpreted to include any propagatingsignals. A computer-readable medium of the subject invention can be, forexample, a compact disc (CD), digital video disc (DVD), flash memorydevice, volatile memory, or a hard disk drive (HDD), such as an externalHDD or the HDD of a computing device, though embodiments are not limitedthereto. A computing device can be, for example, a laptop computer,desktop computer, server, cell phone, or tablet, though embodiments arenot limited thereto.

The subject invention includes, but is not limited to, the followingexemplified embodiments.

Embodiment 1

A system for screening and health monitoring of materials, the systemcomprising:

a material embedded with magneto-electric nanoparticles (MENs);

a laser configured to direct incident laser light waves at a target areaof the material;

an optical filter disposed between the laser and the material; and

an analyzer configured to detect characteristics of the laser lightreflected from the material.

Embodiment 2

The system according to embodiment 1, the MENs being comprised of aferromagnetic core.

Embodiment 3

The system according to embodiment 2, the system further comprising apiezoelectric shell surrounding the ferromagnetic core.

Embodiment 4

The system according to any of embodiments 2-3, the ferromagnetic corebeing comprised of cobalt ferrite (CoFe₂O₄).

Embodiment 5

The system according to any of embodiments 2-4, the piezoelectric shellbeing comprised of barium titanate (BaTiO₃).

Embodiment 6

The system according to any of embodiments 1-5, a diameter of the MENsbeing a width within a range of from 10 nm to 100 nm.

Embodiment 7

The system according to any of embodiments 1-6, the first optical filterbeing configured to permit a specific polarization of incident lightwaves to pass from the laser to the material.

Embodiment 8

The system according to any of embodiments 1-7, the laser being a diodelaser.

Embodiment 9

The system according to any of embodiments 1-8, the laser beingconfigured to emit light waves at a wavelength of 408 nm, 532 nm, and650 nm.

Embodiment 10

The system according to any of embodiments 7-9, further comprising asecond optical filter disposed between the material and the analyzer;the second optical filter being configured to permit a specificpolarization of reflected light waves to pass from the material to theanalyzer.

Embodiment 11

The system according to any of embodiments 1-6 or 8, further comprisinga single optical filter having a first surface facing the laser and theanalyzer and a second surface facing the sample surface; the opticalfilter being configured to permit a specific polarization of incidentlight waves to pass through from the laser to the material and reflectedlight waves from the material to the analyzer.

Embodiment 12

The system according to any of embodiments 1-11, the analyzer comprisinga processor in operable communication with a computer-readable mediumhaving instructions stored thereon that, when executed, cause theprocessor to:

detect the a phase change difference between the incident light wavesand the reflected light waves.

Embodiment 13

A system for screening and health monitoring of materials, the systemcomprising:

a material embedded with magneto-electric nanoparticles (MENs);

a conductive coil disposed at a target position on a surface of thematerial;

a power source electrically connected to the conductive coil; and

an analyzer configured to detect the magnetic characteristics of theconductive coil.

Embodiment 14

The system according to embodiment 13, the MENs being comprised of aferromagnetic core and a piezoelectric shell surrounding theferromagnetic core.

Embodiment 15

The system according to embodiment 14, the ferromagnetic core beingcomprised of cobalt ferrite (CoFe₂O₄).

Embodiment 16

The system according to any of embodiments 14-15, the piezoelectricshell being comprised of barium titanate (BaTiO₃).

Embodiment 17

The system according to any of embodiments 13-16, a diameter of the MENsbeing a width within a range of from 10 nm to 100 nm.

Embodiment 18

The system according to any of embodiments 13-17, the conductive coilbeing a single turn coil.

Embodiment 19

The system according to any of embodiments 13-17, the conductive coilbeing a multi-turn coil.

Embodiment 20

The system according to any of embodiments 13-19, the power source beingconfigured to transmit an alternating current (AC) signal to theconductive coil in a range of from 100 Hz to 1 GHz.

Embodiment 21

The system according to any of embodiments 13-20, the analyzer furthercomprising a processor in operable communication with acomputer-readable medium having instructions stored thereon that, whenexecuted, cause the processor to:

cause an alternating current (AC) signal to be transmitted to theconductive coil in a range of from 100 Hz to 1 GHz;

detect a signal response over the range; and

generate an M-H hysteresis loop.

Embodiment 22

A system for screening and health monitoring of materials, the systemcomprising:

a material embedded with magneto-electric nanoparticles (MENs); and

a means for detecting a magnetic signal from the material.

Embodiment 23

The system according to embodiment 22, the MENs being comprised of aferromagnetic core and a piezoelectric shell surrounding theferromagnetic core.

Embodiment 24

The system according to embodiment 23, the ferromagnetic core beingcomprised of cobalt ferrite (CoFe₂O₄).

Embodiment 25

The system according to any of embodiments 23-24, the piezoelectricshell being comprised of barium titanate (BaTiO3).

Embodiment 26

The system according to any of embodiments 22-25, a diameter of the MENsbeing a width within a range of from 10 nm to 100 nm.

Embodiment 27

The system according to any of embodiments 22-26, the means comprising:

a laser configured to direct incident laser light waves at a target areaof the material;

an optical filter disposed between the laser and the material; and

an analyzer configured to detect the laser light reflected from thematerial,

the first optical filter being configured to permit a specificpolarization of the incident light waves to pass from the laser to thematerial, and

the analyzer comprising a processor in operable communication with acomputer-readable medium having instructions stored thereon that, whenexecuted, cause the processor to detect a phase change differencebetween the incident light waves and the reflected light waves.

Embodiment 28

The system according to embodiment 27, the means further comprising:

a second optical filter disposed between the material and the analyzer,

the second optical filter being configured to permit a specificpolarization the reflected light waves to pass from the material to theanalyzer.

Embodiment 29

The system according to any of embodiments 22-27, the means comprising:

a conductive coil disposed at a target position on a surface of thematerial;

a power source electrically connected to the conductive coil; and

an analyzer configured to detect the magnetic characteristics of theconductive coil,

the power source being configured to transmit an alternating current(AC) signal to the conductive coil in a range of from 100 Hz to 1 GHz,and

the analyzer further comprising a processor in operable communicationwith a computer-readable medium having instructions stored thereon that,when executed, cause the processor:

to cause an alternating current (AC) signal to be transmitted to theconductive coil in a range of from 100 Hz to 1 GHz;

detect a signal response over the range; and

generate an M-H hysteresis loop.

Embodiment 30

The system according to any of embodiments 22-27, the means comprising:

a nano-, micro-, or mm-size probe made from a non-magnetic solidmaterial;

a tip of the probe made from a magnetic material;

a piezoelement attached to the probe;

a power source electrically connected to the piezoelement; and

an analyzer,

the power source being configured to apply an AC voltage to thepiezoelement,

the probe being disposed at a constant distance from the material, and

the analyzer being configured to detect a change in a resonant frequencyof the probe.

Embodiment 31

The system according to embodiment 30, the probe being comprised ofquartz.

Embodiment 32

A method for screening and health monitoring of materials, the methodcomprising:

embedding a material with magneto-electric nanoparticles (MENs); and

providing a means for detecting a magnetic signal from the material.

Embodiment 33

The method according to embodiment 32, the MENs being comprised of aferromagnetic core and a piezoelectric shell surrounding theferromagnetic core.

Embodiment 34

The method of embodiment 33, the ferromagnetic core being comprised ofcobalt ferrite (CoFe₂O₄).

Embodiment 35

The method according to any of embodiments 33-34, the piezoelectricshell being comprised of barium titanate (BaTiO₃).

Embodiment 36

The method according to any of embodiments 32-35, a diameter of the MENsbeing a width within a range of from 10 nm to 100 nm.

Embodiment 37

The method according to any of embodiments 32-36, the means comprising:

a laser configured to direct incident laser light waves at a target areaof the material;

an optical filter disposed between the laser and the material; and

an analyzer configured to detect the laser light reflected from thematerial,

the first optical filter being configured to permit a specificpolarization of the incident light waves to pass from the laser to thematerial, and

the analyzer comprising a processor in operable communication with acomputer-readable medium having instructions stored thereon that, whenexecuted, cause the processor to detect a phase change differencebetween the incident light waves and the reflected light waves.

Embodiment 38

The method according to embodiment 37, the means further comprising:

a second optical filter disposed between the material and the analyzer,

the second optical filter being configured to permit a specificpolarization the reflected light waves to pass from the material to theanalyzer.

Embodiment 39

The method according to any of embodiments 32-36, the means comprising:

a conductive coil disposed at a target position on a surface of thematerial;

a power source electrically connected to the conductive coil; and

an analyzer configured to detect the magnetic characteristics of theconductive coil,

the power source being configured to transmit an alternating current(AC) signal to the conductive coil in a range of from 100 Hz to 1 GHz,and

the analyzer further comprising a processor in operable communicationwith a computer-readable medium having instructions stored thereon that,when executed, cause the processor:

to cause an alternating current (AC) signal to be transmitted to theconductive coil in a range of from 100 Hz to 1 GHz;

detect a signal response over the range; and

generate an M-H hysteresis loop.

Embodiment 40

The method according to any of embodiments 32-36, the means comprising:

a nano-, micro-, or mm-size probe made from a non-magnetic solidmaterial;

a tip of the probe made from a magnetic material;

a piezoelement attached to the probe;

a power source electrically connected to the piezoelement; and

an analyzer,

the power source being configured to apply an AC voltage to thepiezoelement,

the probe being disposed at a constant distance from the material, and

the analyzer being configured to detect a change in a resonant frequencyof the probe.

A greater understanding of the present invention and of its manyadvantages may be had from the following example, given by way ofillustration. The following example is illustrative of some of themethods, applications, embodiments and variants of the presentinvention. The example is, of course, not to be considered as limitingthe invention. Numerous changes and modifications can be made withrespect to the invention.

Example 1

Basic room-temperature M-H hysteresis loops of 30-nm MENs integratedinto an adhesive bond (in the shape of a rectangular slab) duringdifferent stages of treatment and measured via vibrating samplemagnetometery for an in-plane orientation are shown in FIG. 5.Comparative M-H curves in an in-plane (IP) orientation of MENsintegrated into an adhesive bond during different stages of treatment atroom temperature are shown in FIG. 5.

It can be noted that the nanoparticles induce almost an order ofmagnitude weaker signal after the bond is exposed to an ultraviolet (UV)waves. It should be mentioned that the signal measured through VSMdirectly reflects the quality of the bond in the vicinity of thenanoparticles and thus provides a quality control at the nanoscale.Similarly, under different treatment conditions, the signal could alsogo up by orders of magnitude.

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication.

All patents, patent applications, provisional applications, andpublications referred to or cited herein (including those in the“References” section, if present) are incorporated by reference in theirentirety, including all figures and tables, to the extent they are notinconsistent with the explicit teachings of this specification.

What is claimed is:
 1. A system for screening and health monitoring ofmaterials, the system comprising: a material embedded withmagneto-electric nanoparticles (MENs); a laser configured to directincident laser light waves at a target area of the material; a firstoptical filter disposed between the laser and the material; and ananalyzer configured to detect a structural defect by measuring amagnetization at a local region of the material by detecting a change inlight intensity between the incident laser light and laser lightreflected from the local region of the material.
 2. The system of claim1, the MENs being comprised of a ferromagnetic core and a piezoelectricshell surrounding the ferromagnetic core.
 3. The system of claim 1, theferromagnetic core being comprised of cobalt ferrite (CoFe₂O₄).
 4. Thesystem of claim 1, the piezoelectric shell being comprised of bariumtitanate (BaTiO₃).
 5. The system of claim 1, a diameter of the MENsbeing a width within a range of from 10 nm to 100 nm.
 6. The system ofclaim 1, the first optical filter being configured to permit a specificpolarization of the incident light waves to pass from the laser to thematerial.
 7. The system of claim 1, the laser being a diode laser. 8.The system of claim 1, the laser being configured to emit light at awavelength of 408 nm, 532 nm, and 650 nm.
 9. The system of claim 6,further comprising a second optical filter disposed between the materialand the analyzer; the second optical filter being configured to permit aspecific polarization of the reflected light waves to pass from thematerial to the analyzer.
 10. The system of claim 1, the analyzer beingfurther configured to detect a structural defect by measuring amagnetization at a local region of the material by detecting a phasechange between a phase of the incident laser light and a phase of thelaser light reflected from the local region of the material.
 11. Asystem for screening and health monitoring of materials, the systemcomprising: a material embedded with magneto-electric nanoparticles(MENs) comprised of a ferromagnetic core and a piezoelectric shellsurrounding the ferromagnetic core; a diode laser configured to directincident laser light waves at a target area of the material; a firstoptical filter disposed between the diode laser and the material; asecond optical filter disposed between the material and the analyzer;and an analyzer configured to detect a structural defect by measuring amagnetization at local region of the material by either: detecting achange in light intensity between the incident laser light and the laserlight reflected from the local region of the material; or detecting achange between a phase of the incident laser light and a phase of laserlight reflected from the local region of the material, the ferromagneticcore being comprised of cobalt ferrite (CoFe₂O₄), the piezoelectricshell being comprised of barium titanate (BaTiO₃), a diameter of theMENs being a width within a range of from 10 nm to over 100 nm, thefirst optical filter being configured to permit a specific polarizationof incident light waves to pass from the laser to the material, and thesecond optical filter being configured to permit a specific polarizationof reflected light waves to pass from the material to the analyzer.